In wireless communication networks of the third generation of which the UMTS (Universal Mobile Telephony System) is an example, user traffic is forwarded from a GGSN (Gateway GPRS Support Node) and a SGSN (Serving GPRS Support Node) via the RNC (Radio Network Controller) to one or more BSs (Base Stations) and finally to one or more UEs (User Equipments). User traffic may also be transmitted via an external PDN (Packet Data Network) via the previous nodes to the UE.
In the remaining part of the description, BSs, which in wireless networks of the third generations comprise Node B's, will simply be referred to as RBSs (Radio Base Stations).
In UMTS networks the role of the GGSN and SGSN is more of a data packet router, while the RNC is controlling the use of radio resources in the wireless communication network.
Here, the lub interface is the communication interface over which the user data is exchanged between the RNC and the RBS. User data transmission and reception between an RBS and a UE (User Equipment), however, is handled over the Uu interface which is the air interface between the RBS and the UE.
These interfaces are illustrated in FIG. 1.
Data transmission between an RNC (or SRNC) and a Radio Base Station (RBS) and between an RBS and one or more UEs (User Equipments) usually proceeds by transmitting one or more PDUs (Packet Data Units) from a PDU buffer (PDU Bf) in the RNC to a PDU buffer in the RBS and further from a PDU buffer in the RBS to a UE In an HSDPA scenario, packet buffers in a base station transceiver are called PQs (Priority Queues). One illustration of this is given in FIG. 2
Now, specifically in WCDMA RAN HSDPA (Wideband Code Division Multiple Access Radio Access Network High-Speed Downlink Packet Access) wireless communication networks, part of the user plane traffic over the lub interface is regulated by a flow control algorithm at the Framing Protocol level. Using flow control, an RBS can, depending on bitrate capacity over the air interface Uu and possible congestion over the lub interface, instruct the RNC to vary the data rate delivered to the RBS and belonging to a certain data flow. This the RBS does by transmitting CA (Capacity Allocation) control frames defining the maximum available data rate for data transmission from the RNC to the RBS via the lub interface.
In this fashion, more PDUs per time unit (or higher data rates) can be made available to those data flows which show good connection quality leading to higher packet data rates experienced at the specific UE.
Hence the main goal for the flow control is to ensure that the RNC provides the RBS with the correct amount of data packets in PQs. A low amount of data from the RNC may lead to PQs in the RBS becoming empty and the air interface capacity not utilized fully. On the other hand, a high amount of data from the RNC may cause the HSDPA scheduler not be able to schedule data in time so that data becomes too old in the. Also, if PQs are allowed to grow too much, retransmission from PDU buffers in the RNC would take longer.
From a flow control point of view there are two types of bottleneck for the HS (High-Speed) data flow in a HSDPA-based wireless communication network, namely the lub and Uu interfaces. lub interfaces normally have an essentially fixed maximum available bandwidth or maximum available bitrate capacity which under normal circumstances does not vary. When the bottleneck is reached, e.g. when the transmitted bitrate is higher than the bottleneck bitrate) the RBS starts receiving incorrect or delayed data frames from the RNC.
In contrast to the lub interface, the maximum available bandwidth over the Uu interface can vary drastically. The most significant source of the drastic bandwidth changes over the Uu interface consists of changing air-interface conditions and the fast channel dependent modulation and coding to account for these changing conditions.
These two types of bottlenecks, i.e. lub congestions and Uu congestions, should be treated in different ways. In HSDPA-networks, fairness on the lub interface is handled by HSDPA flow control and by a HSDPA scheduler for the Uu interface. As a consequence, it is important for the CA bitrate (data rate requested from an RBS to the RNC) to follow air-interface performance variations in a good and fast way. Present solutions have the drawback that Uu congestions are treated in an lub congestion detection fashion, i.e. using the linear data rate increase also after a Uu congestion detection, which is not optimal.
In solutions known from existing technology, it is possible to increase the CA bitrate with a boosting factor when no lub congestion occurs. The increase rate is then higher than the linear increase rate which is used after an lub congestion. Boosting is used if the amount of data in the PQs becomes too low. This ensures that PQs will be filled with data rapidly if the air-interface performance is improved so that higher data rate can be used to the UE.
However, in solutions used in known technology, when an lub congestion occurs, the intention is that only linear increase shall be allowed for a while so that the lub bottleneck isn't exceeded again too quickly. Therefore a timer is set to prevent the faster increase with a boosting factor mentioned above (when PQs gets empty).
The drawback with this solution is for fast fluctuating air-interface conditions when the CQI changes rapidly and after an lub congestion has been detected. Usually, (when no lub congestions have been detected) a decrease in CA bitrate due to Uu congestion can be followed by an increase with the boosting factor if the air-interface conditions change quickly. This is not allowed after an lub congestion so that PQs run empty and the air-interface capacity is not fully used.
The present invention aims at solving at least some of the disadvantages related to known technology.